Host processor systems may store and retrieve data using storage devices containing a plurality of host interface units (host adapters), disk drives, and disk interface units (disk adapters). Such storage devices are provided, for example, by EMC Corporation of Hopkinton, Mass. and disclosed in U.S. Pat. No. 5,206,939 to Yanai et al., U.S. Pat. No. 5,778,394 to Galtzur et al., U.S. Pat. No. 5,845,147 to Vishlitzky et al., and U.S. Pat. No. 5,857,208 to Ofek, which are incorporated herein by reference. The host systems access the storage device through a plurality of channels provided therewith. Host systems provide data and access control information through the channels of the storage device and the storage device provides data to the host systems also through the channels. The host systems do not address the disk drives of the storage device directly, but rather, access what appears to the host systems as a plurality of logical volumes. Different sections of the logical volumes may or may not correspond to the actual disk drives.
Data striping is a technique of segmenting logically sequential data so that segments can be assigned to multiple disk drives or other physical devices in a round-robin fashion and thus written concurrently. Data striping may be used in connection with RAID (redundant array of independent disks) storage systems and may be useful in situations where a processor is capable of reading or writing data faster than a single disk can supply or accept it. Specifically, in connection with accessing data that has been striped, while one data segment is being transferred from the first disk, a second disk can locate the next segment. Known management systems allow for the adjustment of the coarseness of the striping pattern and data striping may be used separately from or in conjunction with data mirroring techniques. Advantages of striping include improvements in performance and throughput.
Logical devices containing the data that has been stored across multiple disk drives may be accessed at different frequencies. Access density is the ratio of performance, measured in I/Os per second, to the capacity of a disk drive, e.g., measured in gigabytes (Access Density=I/Os per second per gigabyte). Increasing capacity of a disk drive, without a corresponding improvement in performance at the drive level, creates a performance imbalance that may be characterized by the access density. In attempts to maintain acceptable performance levels as disks get larger, allocation levels within disks may be used that lead to inefficient utilization of the disks. That is, end-users may allocate less space per disk drive to maintain performance levels and may add more disk drives to support increased activity levels and capacity. These actions may add costs to the infrastructure and/or to operational expenses. Access density may be significant factor in managing storage system performance and the tradeoffs of using higher-capacity disks may be carefully evaluated in view of the possibility of lowering access performance versus adding higher performance disk drives that may be expensive. Users may balance performance, capacity and costs when considering how and whether to replace and/or modify a storage array.
Accordingly, it would be desirable to provide a system that may advantageously facilitate the optimization of performance, capacity and cost characteristics of storage resources in a multi-tier storage environment.